High power waveguide windows



Jan. 23, 1962 E. c. oKREss ETAL HIGH POWER WAVEGUIDE wINDows 5 Sheets-Sheet 1 Filed Dec. 1l, 1953 5 T5151. 50A, T5

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vf/ /ZZ E. C. OKRESS ETAL HIGH POWER WAVEGUIDE WINDOWS 1NVENTOR5, ERNEST C. Ofc/esas L50 C. WERNER Il f f Jan. 23, 1962 Filed Deo. 11. 195s I I I I l l I IIT lill. 1/

TH# E Jan. 23, 1962 E. c. oKRl-:ss ETAL 3,018,453

HIGH POWER WAVEGUIDE WINDOWS Filed Dec. 1l. 1953 5 Sheets-Sheet f4 347 0K 504 .5T/UNLESS .STEEL N500/N6 LIP fa zal Jan. 23, 1962 E. c. oKREss ETAL 3,018,453

HIGH POWER WAVEGUIDE WINDOWS Filed Dec. l1, 1953 5 Sheets-Sheet 5 OXYGEN-FREE H/VNEHLEP :UPPER INVENTORS. Een/sr C. o/sss Eo C. WER/ven v asians Patented Jan.` 23, 1 962 3,018,453 HIGH PGWER WAVEGUHDE WlNDGWS Ernest C. Oltress, Montclair, and Leo C. Werner, Cedar Grove, NJ., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Dec. 11, 1953, Ser. No. 397,806 21 Claims. (Cl. S33-9S) This invention relates to high power waveguide windows and more particularly to improved waveguide window assemblies for use adjacent the output of a high power magnetron.

In microwave systems magnetrons are used generally for generating the high frequency electromagnetic energy. To transfer this energy from the magnetron to a load which load can be an antenna system or the like, waveguide means are connected to the magnetron and the load. The high frequency electromagnetic energy generated in the magnetron is channeled through the waveguide means to the antenna system. Several problems are encountered in utilizing a waveguide for channeling electromagnetic energy between a magnetron and an antenna system. For example, provision needs to be made for maintaining the evacuated condition within the magnetron cavity. Another problem that needs to be resolved is the proper matching of the impedance of the magnetron having an order of magnitude of a few ohms to that of the waveguide means having an impedance of the order of magnitude of several hundred ohms. Additionally the heat radiated by the magnetron cathode requires special attention in designing the portion of the waveguide immediately adjacent thereto. One of the expedients employed to accomplish proper matching is an H type transformer positioned between a resonant cavity of the magnetron and the waveguide coupled into said resonant cavity. To maintain the vacuum within the magnetron when a waveguide is coupled into one of its resonant cavities resort is had to a waveguide window. The window is made of a material which is impervious to the passage of gases and the periphery of said window is hermetically sealed to the inside surface of the waveguide. The waveguide window is preferably located proximate to the matching transformer between the magnetron and the waveguide. Ideally the window offers no impedance to the passage of electromagnetic wave energy but in practice this is not attained. To meet operational requirements the waveguide window must be able to withstand the dielectric losses in the window due to the small interceptio-n of microwave energy from the magnetron and the radiated heat of the magnetron cathode which reaches it through the H matching transformer. In the latertypes of high power magnetrons the cathode operates at a temperature ranging from 1300 to l600 C. the amount of heat radiated by the high power magnetron cathodes operating at these temperatures and even at times up to l700 C. present a very special problem in the provision of waveguide windows which can stand up under high power operation and when the window opposite the Vacuum is not pressurized, offer minimum electrical mismatch and operate efficiently for a long time.

Waveguide windows presently used are made of a plurality of materials such as glass and various ceramics that are generally known in the art. The existing smaller waveguide windows may be acceptable where they do not have to withstand very high powers without pressurization and high unequal temperature gradients,

This invention represents a departure from the prior art in that it provides window arrangements having such configuration and made of such material that they are capable of withstanding the very high powers and electric 4fields and very high operational temperatures generated by newer types of high power magnetrons. There is further provided in this invention a novel cooling arrangement for glass waveguide windows which cooling arrangement includes an air-circulating system. in one modification of this invention, a more flexible waveguide portion is provided for use under extreme stress conditions and which includes an end portion in the form of a bellows for introducing more flexibility between the waveguide plumbing and the window whereby the window may be safely connected in place.

An object of this invention is to provide a high power waveguide window.

A further object is to provide a waveguide window which is adapted to withstand high unequal temperatures due to nonuniform heat radiation from the magnetron cathode.

A further object is to provide for cooling of a waveguide glass dome window.

A further object is to provide for easier and safer mounting of a waveguide window.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. l is a sectional view of a terminal portion of a waveguide including a preferred embodiment of this invention,

FIG, 2 is a modification of the structural arrangement shown in FG. 1 and including a bellows,

FIG. 3 is a detail view of a modified window subassembly including a rigid skirt having apertures for permitting circulation of cooling air,

FIG. 4 is a View of a modified window subassembly which may be substituted in the terminal portion of waveguide shown in FIG. l, and

FIG. 5 is an assembly view including a flat ceramic window.

In FIG. 1 there is shown a transducer 11 of a waveguide 13 adapted for connection to a magnetron, not shown. Waveguide 13 is preferably circular in cross section; the circular form is preferred because of its higher power capacity and because it provides desirable geometry for the window. Between the magnetron, not shown, and the waveguide is conventionally disposed a transformer 14 such as an H-transformer having an inlet 14A adapted for communication with a magnetron cavity. The section of waveguide 13 shown is hermetically sealed in conventional manner to maintain the evacuated condition within the adjoining magnetron. A tubular housing section 15 is concentrically mounted relative to waveguide 13 by means of a flange 19 to remove waveguide stresses from the window when coupling the waveguide 13 to the system waveguide. Secured toward the right hand end of the waveguide 13 as seen in FIG. 1 forming an integral extension thereof is a cylindrical section 16 made of an alloy known as Kovar and bonded to the inner surface of section 16 of Kovar and coaxial therewith is a dome-shaped glass window 17 preferably of type 7070 commercial glass. The actual bonding between the window 17 and the section 16 of Kovar is through a small section 18 of type 7050 commercial glass. A good bond characterized by an hermetic seal is achieved in bonding Kovar and type 7050 glass. The dome-shaped window portion 17 is very thin having an order of magnitude of about 1/16 to ls inch as compared with the much larger waveguide within which it may be used. The Sagitta of the dome-shaped portion 17 is substantially equal to the radius of the waveguide 13. Though the dome-shaped window is made of thin glass, it effectively withstands atmospheric pressure in an analagous'v manner to that of an ordinary light bulb because of its geometry; it also provides a good electrical match.

There is secured within the waveguide section 13 an iris 20 to correct for mismatch due to the presence of the dome-shaped window. The dimensions of the iris and its spacing from the end of the dome-shaped window is based upon conventional electrical matching considerations well known to the art. A coupling flange 22 is provided to provide electrical continuity between transducer 11 and the system waveguide leading to the load. The air circulating attachment 23 provides a means for sweeping out the ionized air adjacent to the window due to the very high intensity of the electric field as well as a temperature-control means. The attachment 23 is arranged immediately adjacent the dome-shaped window 17 on the side away from the magnetron for directing cooling air about the surface of the dome-shaped window during very high power operation. The attachment 23 comprises a first cylindrical portion 24 formed with two circular series of bores 25. The sloping bores 25 in portion 24 are not in radial planes, but are skewed laterally so as to set up a swirl of air around the dome 17. Secured to the flange 27 of the cylindrical portion 24 is a short tubular manifold 28. A stub 32 is tangentially joined to the manifold 28 to communicate peripheraily with an opening 29 formed in manifold 28. A ring 33 is secured to the opposite end of the short cylindrical section of manifold 28 and is in turn secured to another short cylindrical section 34. The short cylindrical section 34 is seated in the step 35 of the cylindrical portion 24. By means of this assembly a source of air (not shown) may be connected to the short cylindrical stub 32 to circulate air at about 100-200 cu. ft./hr. through the annular channel 36 for distribution through the skewed apertures 25 so as to set up a swirl of air around the surface of the dome-shaped window. The entire assembly is characterized by long life and high eciency at high power operation.

A modified structural arrangement is shown in FIG. 2 and is for use under extreme service conditions. A flexible bellows 37 not included in the assembly of FIG. 1 is secured between the section 16 of Kovar and the coupling joint 23. The purpose of the bellows 37 is to incorporate much greater flexibility between the waveguide plumbing and the dome-shaped window so as not to damage the window in the process of connecting the associated sections of waveguide and also so as not to damage the window in use under extreme service conditions, which are not usually encountered because of the care made necessary by other components of the system. The bellows 37 serves as a yieldable guard overlying the window. Instead of the air circulating attachment 23 shown in FIG. 1, several circular series of apertures 38 are provided in the adjacent convolutions of the bellows 37. It is to be noted that each of the circular series of apertures 38 are provided on the sides of the convolutions which directs the air against the surface of the window 17 upon entering the waveguide. The air inlet stub 32' is tangentially connected to tubular housing section coaxial with and surrounding the section of waveguide. The air inlet stub 32 communicates peripherally with an opening 31 formed in the tubular housing section 15' to cause the cooling air to circulate around the waveguide. Bellows 37 provides a flexible joint between window frame 16 and hence the window 17 and coupling 23. It also provides electrical continuity for the electromagnetic waves flowing through the pipe.

The air-cooling arrangement shown in FIG. 2 wherein the compressed air is introduced into the annular chamber between the outer tubular housing section 15 and the circular waveguide has the important advantage of' not being as heavy as the arrangement shown in FIG. 1.

In the modified arrangement shown in FIG. 3 the bellows 37 is replaced by a rigid tubular member 40. The

tubular member 40 that forms a cylindrical skirt is pro vided with several circular series of apertures 41. The cylindrical section 4() protects the glass window from breakage during installation in the same manner as does the bellows 37 shown in FIG. 2 even though it does not have the greater yieldability of the bellows. However, it is much simpler and is less likely to become a site of electric breakdown.

A further modification of dome-shaped window is shown in FIG. 4 wherein the dome is formed of a stack of rings, the different rings being of different compositions of glass to afford gradual expansion characteristics and match the heat resistant Vycor dome to the Kovar cylinder.

Where it is desired to use a flat disc-like ceramic window instead of a dome-shaped glass or ceramic window as shown in the device of FIG. 1 an assembly arrangement as shown in FIG. 5 may be employed. A flat discshaped ceramic window has an advantage over a domeshaped window in that it has a much higher softening temperature, lower dielectric loss, and is reproducible electrically to a high order. A window in the form of flat disc 44 is mounted in the same relative position as is the dome-shaped window in FIG. 1. A matching disc 45 is connected Iby a single radial rod (not shown) to the inside of the waveguide. The radial rod is in a plane including the axis of the waveguide, which plane is normal to the plane of polarization of the dominant circular waveguide mode. The disc 45 is provided for electrically matching the window 44. The disc 45 also thermally shields the at disc-like ceramic window from the direct heat radiation emanating from the magnetron cathode, not shown. This type of matching arrangement is disclosed in copending application Serial No. 397,805, filed December 11, 1953, now Patent No. 2,817,823, by Ernest C. Okress, for Circular Waveguide Output for Magnetrons. This matching arrangement is described in the above application as a lollypop matching device. Considerably less heat attributable to direct radiation from the magnetron cathode reaches the surface of the window disc 44 because of the shielding action of matching disc 45. The thermal radiation absorption of ceramic discs are greater than for glass windows of the same mass and hence the disc 44 would tend to heat up more and unevenly if it was not protected by the disc 45.

Ceramic windows illustrated by FIG. 5 could be electrically matched by the transformer 14 of FIG. 1 and FIG. 5, without resort to the matching devices (i.e. iris, plug, disc, etc.) illustrated by FIG. 1 and FIG. 5. The glass dome windows illustrated by FIGS. 1, 2, 3, and 4 cannot be reproduced with sutlicient accuracy commercially to justify use of the transformer 14 in FIG. 1 in preference to the simpler and adjustable iris 20 of FIG. 1 for purposes of matching the window.

In operation the various preferred arrangements of transducers with the windows therefor allow for eflicient joining of higher power magnetrons to a waveguide systern. The glass dome-shaped window is characterized by a low impedance to the transfer of electromagnetic wave energy, ruggedness and a high strength for resisting atmospheric pressure plus heat resisting characteristics. The air circulating arrangements for permitting air to circulate about one surface of the windows make possible the close proximity of the window to the high power magnetron. The bellows 37 shown in FIG. 2 and its equivalent cylindrical section 40 shown in FIG. 3 serve not only to provide apertures for the passage of compressed air across the surface of the window but also to guard the window against breakage during installation. The improved window assemblies of this invention are characterized by ruggedness, greater efficiency and longer life; the junction between a waveguide and a high power magnetron is thereby made durable and eicient.

Obviously many modifications and variations of the present invention are possible inthe' light of the above' teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

l. A waveguide comprising a waveguide section having an inlet at one end through which waves are received, a window sealed across said section at a part thereof remote from said inlet in the direction in which the waves travel, means located in said section beyond said window in the direction of wave travel and solely along the passage of the section, for directing jets of air against the adjacent face of said window to limit increases in the temperature of said window during use and to sweep away from said window any ionized air that may be accumulated there.

2. The waveguide defined in claim 1 in which said waveguide section is circular in cross section.

3. The waveguide of claim 1 in which said window is fiat.

4. The waveguide of claim 1 in which said window is dome-shaped.

5. The waveguide as defined in claim 1 further comprising a thermal radiation shield between the inlet and said window to' prevent thermal radiation from reaching said window. A, y V

l6.,'lhe waveguide as defined in claimvl further cornprising asecond section of waveguide, and a fiexible bellows sealed to one end of said second' section of waveguideland ,sealed to the. end of .the first said waveguide section opposite its inlet end.

7. The waveguide as defined in claim'l further comprising a'second section of waveguide, and a liexible cylindrical skirt sealed to one end of said second section of waveguide and sealed to the end of the first said waveguide section opposite its inlet end.

8. A waveguide window for attachment to a waveguide cylindrical section by a glass sealing alloy and cornprising; a dome-shaped portion of high heat resistant glass, a plurality of ring-like portions of glass having their rims bonded to each other, and to the rim of said dome-shaped portion and providing a continuation of the inside and outside surfaces of said dome-shaped portion, said ring-like portions being of different compositions and providing gradual heat expansion characteristics progressively approaching the heat expansion characteristic of said alloy, the free edge of said ring-like portion that forms the free edge of the connected rings and which is furthest from said domesshaped portion terminating in a circular cylindrical edge surface of relatively short length compared to the total length of said window by which said window may be bonded and sealed to the inside surface of said cylindrical portion of a waveguide.

9. A waveguide window for attachment to a waveguide section by a glass sealing alloy, comprising; a hernispherical shaped portion of high heat resistant glass; a rst ring of another heat resistant glass of the same wall thickness and of the same diameter as the rim of said hernispherical shaped portion and bonded to said hernispherical shaped portion to provide a continuous eX- tended inside and outside surface with said hernispherical portion; a second ring of still another heat resistant glass of the same wall thickness and of the same diameter as said first ring and bonded along an edge thereof to an edge of said first ring to provide therewith a continuous inside and outside surface; a third ring of a further heat resistant glass of the same wall thickness and of the same diameter as said second ring and bonded edgewise to said second ring to provide therewith a continuous inside and outside surface; and a fourth ring having a rim that is of the same wall thickness and of the same diameter as said third ring and bonded edgewise thereto to provide a continuous inside and outside surface, said rings being of different compositions and having heat expansion characteristics varying progressively from near that of said hernispherical portion to approximately that of said alloy, the inside and outside surfaces of said fourth ring increasing in diameter across that ring in a direction away from said third ring, and terminating in a circular cylindrical outside surface of relatively short length compared to the total length of said window, which cylindrical surface may be bonded and sealed to the interior cylindrical surface of a waveguide.

V10. A waveguide comprising; a section of circular waveguide having an inlet at one end; a window disposed across and closing the interior of said waveguide beyond said inlet in the direction of wave travel; said window including a dome-shaped portion and a ring-like portion of high heat resistant glass, bonded together edge to edge, with said ring-like portion having its inside surface and its outside surface forming a continuation of the inside surface and the outside surface respectively of said dome-shaped portion, said ring-like portion terminating, at its edge that is unconnected to said dome-shaped portion, in a cylindrical wall, of relatively short length compared to the total length of said window, said ring-like portion having a thermal expansion characteristic nearer to that of a glass sealing alloy than said dome-shaped portion, the circular cylindrical outside surface of said window being bonded and sealed to the inside surface of said section of circular waveguide by a glass sealing alloy. 11'. A waveguide as defined in claim 10 further comprisinga second section of circular waveguide, a circular fi'e'Xible means at least approximately as large in diameter as said window connected to the end of the first said section of said circular waveguide opposite from its inlet end and also connected to one end of said second section of waveguide.

12. A waveguide as dened in claim 11 wherein said flexible means in the portion adjacent said window is perforated and through which streams of a cooling duid may be directed against said window to prevent the eX- istence of very high temperature of said window during use.

13. A waveguide as defined in claim 12 further comprising air circulating means provided adjacent one of said sections of waveguide and adjacent the window for directing air through the perforations toward the surface of said window opposite from said inlet for limiting the temperature of said window and for limiting air ionization around the outer surface of said window.

14. A waveguide comprising an enclosedr conduit along the interior of which the waves travel, and having across its interior a restricted inlet through which the waves pass, a window disposed across and closing the interior of said conduit beyond said inlet in the direction in which said waves travel but intermediate of its ends, said window being largely ceramic and sealed to the interior surface of said conduit, said conduit in the portion just beyond said window in the direction in which the waves travel having passages in its wall directed toward the window for directing fluid streams against the window to control the temperature of the window during use without materially obstructing said interior of said conduit.

15. The waveguide as set forth in claim 14, wherein said conduit is provided with a closed annular supply passage surrounding it and communicating with the outer ends of said wall passages to supply thereto iiuid under pressure, and an inlet tube opening into said annular supply passage for connection to a source of uid under pressure.

16. A waveguide comprising a peripherally enclosed conduit having an interior passage along which the waves travel and having a partition across said passage with a restricted inlet through which the waves pass, said conduit beyond said inlet in the direction in which the waves travel having one section with spaced apart inner and outer metallic shells connected at their ends adjacent the inlet, said inner shell adjacent the end opposite from said inlet having a ceramic window extending across and closing it and sealed to the inner periphery of said inner shell to form a closed barrier across said passage, said inner shell at the end remote from said inlet being connected to the outer shell by a exible sleeve permitting limited endwise expansion of the inner shell relatively to the outer shell and provide sufficient eXibility in the conduit to protect said window.

17. The waveguide as set forth in claim 16, wherein said exible sleeve is a bellows.

18. The waveguide as set forth in claim 17, wherein said bellows is provided with fluid passages that pass through the corrugations of said bellows and direct uid streams toward said window.

19. The waveguide as set forth in claim 16, and a matching disc of a diameter considerably smaller than the internal diameter of the inner shell, disposed in a position crosswise of and intersecting the longitudinal axis of said inner shell, for electrically matching the said window and shielding the window somewhat from the direct heat radiation along said passage.

20. A waveguide comprising a peripherally enclosed conduit having an interior passage along which the waves travel and having a partition across said passage with a restricted inlet through which the waves pass, said conduit beyond said inlet in the direction in which the Waves travel having one section with spaced apart inner and outer metallic shells connected at their ends adjacent the inlet, said inner shell adjacent the end opposite from said inlet having a ceramic window extending across and closing it and sealed to the inner periphery of said inner shell to form a closed barrier across said passage, said window having its central portion dome shaped, with the dome extending somewhat along the conduit passage in the direction in which the waves travel, said conduit just beyond said window in the direction in which said waves travel having uid conveying passages opening into said conduit passage for directing fluid streams toward said window to cool said window during use.

21. A waveguide comprising a peripherally enclosed conduit having an interior passage along which the waves travel and having a partition across said passage with a restricted inlet through which the Waves pass, said conduit beyond said inlet in the direction in which the waves travel having one section with spaced apart inner and outer metallic shells connected at their ends adjacent the inlet, said inner shell adjacent the end opposite from said inlet having a ceramic window extending across and closing it and sealed to the inner periphery of said inner shell to form a closed barrier across said passage, said conduit in the portion thereof beyond said window in the direction in which the waves travel having fluid conveying passages opening into said conduit passage for directing streams of a cooling fluid toward said window during use of the guide.

References Cited in the file of this patent UNITED STATES PATENTS 1,956,396 Moran Apr. 24, 1934 2,407,069 Fiske Sept. 3, 1946 2,561,130 McClellan July 17, 1951 2,678,404 Sorg May 11, 1954 OTHER REFERENCES Article by I. C. Turnbull, R.C.A. Review, September 1952 pages 291-299.

Nelson: abstract of application Serial Number 107,583, published October 14, 1952. 

